http status code 404 - Httpwebrequest retrieve large data from Exchange public folder -

i having trouble retrieving data larger 200mb exchange public folder: return "http error 500 internal server error", tried change timeout , size limit in iis , exchange server still not working. have ideas? here code:

using system; using system.collections.generic; using system.linq; using system.text; using system.net; using system.io;  namespace httpgetitem { class program {     static void main(string[] args)     {         string url = "https://pdc/public/-flaturlspace-/5526a9cc936bd54d93ee89bab89f8ff4-36249d11180/5526a9cc936bd54d93ee89bab89f8ff4-3e1f32ef73e";         int timeout = 3600000 * 2;         string = httppost.getresponseasstring(url, timeout);      } }  public class httppost {     static public string getresponseasstring(string url, int timeout)     {       //  httpwebrequest webrequest = (httpwebrequest)system.net.webrequest.create(url);         httpwebrequest webrequest = (system.net.httpwebrequest)httpwebrequest.create(url);         if (url.tolower().startswith("https:"))             system.net.servicepointmanager.certificatepolicy = new trustallcertificatepolicy();           credentialcache mycredentialcache = new credentialcache();         mycredentialcache.add(new system.uri(url),             "ntlm",             new system.net.networkcredential(getusername(), getpassword(), getdomain())             );         mycredentialcache.add(new system.uri(url),             "basic",             new system.net.networkcredential(getusername(), getpassword(), getdomain())             );          webrequest.method = "get";          webrequest.headers.add("translate", "f");         webrequest.contenttype = "application/octet-stream";         webrequest.allowautoredirect = true;         webrequest.timeout = timeout;         webrequest.readwritetimeout = 3600000 * 2;         webrequest.useragent = "mozilla/4.0 (compatible; msie 5.01; windows nt 5.0)";         webrequest.preauthenticate = true;         webrequest.credentials = mycredentialcache;       //  webrequest.proxy = new system.net.webproxy("your proxy server", true); // comment out if you're not going thru proxy          webresponse webresponse = null;          try         {             webresponse = webrequest.getresponse();                stream stream = webresponse.getresponsestream();          //   stream stream = webrequest.getresponsestream();              encoding encoding = system.text.encoding.getencoding("utf-8");              streamreader streamreader = new streamreader(stream, encoding);              string result = streamreader.readtoend();             return result;         }         catch (webexception e)         {              string message = e.message;             if (e.status == webexceptionstatus.protocolerror)             {                 console.write("the server returned protocol error ");                 // httpwebresponse can check http status code.                 httpwebresponse httpresponse = (httpwebresponse)e.response;                 console.writeline((int)httpresponse.statuscode + " - "                    + httpresponse.statuscode);             }              stream exstream = e.response.getresponsestream();             encoding encoding = system.text.encoding.getencoding("utf-8");              streamreader streamreader = new streamreader(exstream, encoding);              string result = streamreader.readtoend();             console.writeline(e.message);             console.writeline(e.stacktrace);             return e.message;         }     }      static public httpwebresponse getresponse(string url)     {          httpwebrequest webrequest = (httpwebrequest)system.net.webrequest.create(url);          //webrequest.proxy = new system.net.webproxy("your proxy server", true); // comment out if you're not going thru proxy         webrequest.allowautoredirect = true;         webrequest.timeout = 1000 * 30;         webrequest.useragent = "mozilla/4.0 (compatible; msie 5.01; windows nt 5.0)";         webrequest.preauthenticate = true;         webrequest.credentials = credentialcache.defaultcredentials;         return (httpwebresponse)webrequest.getresponse();     }   }